Pressurized, saturated steam, particularly centrally generated steam, can be used for many purposes, such as for air humidification, food preparation and for the sterilization of medical devices. The use of pressurized steam, particularly in hospital sterilizers, has given rise to problems, such as stained and spotted sterilized instruments, dirty sterilizers requiring frequent cleaning, malfunctioning of steam-controlled valves, and an excess of maintenance on sterilizer door seals and gaskets. A frequent cause of problems in hospital sterilizers in particular is poor-quality steam; that is, a pressurized, saturated steam that contains particulate matter, such as dirt from the piping system, pipe-scale rust, particles of packings and grease and oil, as well as liquid or condensed water carrying a wide range of contaminants therewith, such as boiler-feed additives, soluble salts and other organic material present in the boiler or water supply, and in addition includes other impurities, such as volatile boiler-feedwater additives, typically volatile alkaline additives, such as amines.
The problems associated with the use of steam, particularly in sterilizers; that is, caused by dirty steam, are often controlled or eliminated by filtering out the solid particulate material and the condensed water or other liquids out of the saturated steam, before the steam enters the sterilizer or is otherwise put to use. Usually, a steam filter is employed, which is an extremely efficient solids filter having a rating of 1 micron or better. Filter tubes composed of a plurality of nonwoven, randomly disposed, borosilicate-glass fibers, having a bonding agent at the fiber-crossover points to form a porous, self-supporting filter tube, have been employed within a filter housing, to provide for a filtered, saturated steam.
The filter tube also contains a bonding agent, such as a silicone resin or fluorocarbon resin, which may be used at the steam temperatures. The filter tube, for example, is placed within a housing within a cylindrical baffle. Unfiltered, saturated, pressurized steam enters the housing through an inlet port and is deflected around the centrifugal baffle, so that the change in direction causes much of the suspended water to drop to the bottom of the housing, from which it is removed automatically by a float-operated drain. The steam is essentially free of condensed water and passes through the walls of the filter tube from the outside inwardly, and filtered steam is removed from the inside of the filter tube through an outlet port and into the sterilizer for use. It has been found that an efficient filter tube can remove virtually all or a substantial portion of the particulate and nonvolatile, water-soluble impurities in saturated steam. However, it is desirable to provide an apparatus and a method for a very highly sterilized steam, particularly for use in hospital sterilizers.